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Plutonium: Environmental Pollution and Health Effects
Plutonium: Environmental Pollution and Health Effects DM Taylor, Institute of Pharmacology, University of Heidelberg, Heidelberg, Germany and Cardiff University, Wales, UK & 2011 Elsevier B.V. All rights reserved.
Abbreviations CL CR FSU ICRP
confidence limit concentration ratio former Soviet Union International Commission on Radiological Protection radioisotope thermoelectric generator standardized incidence ratio United Nations Scientific Committee of the Effects of Atomic Radiation
RTG SIR UNSCEAR
Introduction Plutonium, Element 94, was a primeval element, with gigatonnes of 244Pu and 239Pu being produced by supernova explosions during the creation of the universe and at the genesis of the earth; at that time, their concentration in the earth’s crust was likely to have been of the order of mg kg1. Indeed, 244Pu and 239Pu can be considered to be the parent nuclides of the natural thorium and actinium series, respectively. Since all plutonium isotopes are radioactive (Table 1) with physical half-lives (Tp) that are short in relation to the age of the earth, essentially all the cosmogenic plutonium has now been lost by radioactive decay. It has been estimated that the concentrations of 244Pu in the earth’s crust might be 3 1022 g kg1. However, since the formation of the Table 1
earth, up to B30 kg 239Pu a1 has been produced from 238 U by the spontaneous neutron-capture reaction: 238
b
Uðn;gÞ 239 U -
239
23 min
b
Np -
2:3 d:
239
Pu:
Today the tiny concentrations of 239Pu – B2.1014 g kg1 in the earth’s crust (B80 amol Pu kg1 or B50 mBq 239Pu kg1) – formed through the above reactions, are virtually the only naturally produced plutonium in the environment. The majority of the plutonium currently found in the global environment has arisen since 1945 as the result of human activities, predominantly the development, manufacture, and atmospheric testing of nuclear weapons – by the United States of America, the Former Soviet Union, the United Kingdom, France, and the Peoples Republic of China. Nuclear power production and fuel processing, nuclear waste disposal, and mishaps in nuclear facilities (e.g., the accident at the Chernobyl Nuclear Power Plant in 1986) also made further contributions, but generally on a local rather than a global scale. Another isotope 238Pu has found quite wide application in radioisotope thermoelectric generators (RTG), especially for spacecraft. The burn-up of a 238Pucontaining RTG in the stratosphere above the Indian Ocean, following a failed satellite launch in 1964, caused further worldwide contamination. The plutonium isotopes of greatest environmental interest, 238Pu and 239Pu, decay with the emission of
Some properties of the principal isotopes of plutonium
Nuclide
Half-life (years)
Decay modea (MeV) (% decays)
Specific activity (Bq g1)
Environmental oxidation stateb
Plutonium-238
87.7
6.34 10þ11
IV, V
Plutonium-239
2.4 10þ4
2.30 10þ09
IV, V
Plutonium-240
6563
8.40 10þ09
IV, V
Plutonium-241
14.4
3.81 10þ12
IV, V
Plutonium-244
8.2 10þ7
2.30 10þ6
IV, V
Americium-241
432.7
a 5.456 (28) a 5.499 (72) a 5.105 (12) a 5.143 (15) a 5.156 (73) a 5.124 (27) a 5.168 (73) a 4.897 (0.002) b 0.021 (100) a 4.589 (99.9) SF 0.1% a 5.388 (1) a 5.443 (13) a 5.486 (85)
1.27 10þ11
III
Principal decay mode (low-energy g-ray emission and the fractions of spontaneous fission (SF) of o 0.01% have been ignored). The main oxidation state in soils vegetation and animals, including humans is likely to be IV, but V has been reported in some waters.
a
b
596
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Plutonium: Environmental Pollution and Health Effects
The Distribution and Concentrations of Plutonium in the Environment The available data do not provide a very comprehensive picture of the current levels of plutonium contamination in all parts of the world. It should be recognized that the methods for the determination of plutonium radioactivity are extremely sensitive and some of the concentrations presented in the following text may be orders of magnitude below those that might give concern about human or environmental health. The Global Fallout from Nuclear Weapons Testing The explosion of the second atomic bomb, Fat Boy, above Nagasaki on 9th August 1945 began the widespread release of plutonium into the atmosphere, but by far the largest contribution came from the atmospheric testing of more than 500 atomic and thermonuclear weapons between then and the end of the 1970s. The fallout from such weapons amounted to a total of B250 EBq (2.5 10þ20 Bq) and contained a broad spectrum of radionuclides with half-lives ranging from a few days, 131 I, to many years, including 90Sr, 137Cs and 238Pu, 239Pu, 240 Pu and 241Pu. In the next half-century, most of the shorter-lived radionuclides decayed, leaving only 90Sr and 137Cs, and the plutonium isotopes, as the major fallout nuclides. The amounts of these nuclides dispersed in the atmosphere as a result of nuclear weapons testing are shown in Table 2. The data in Table 2 indicate that the release of a total of B11.5 PBq (1.1 1016 Bq) of 238,239,240 Pu represented only a tiny fraction of the total of Table 2 The amounts of plutonium and some other radionuclides released into the atmosphere by nuclear weapons testing Radionuclide
Plutonium-238 Plutonium-239 Plutonium-240 Plutonium-241 Strontium-90 Caesium-137 Other radionuclides
Estimated release PBq (10þ15Bq)
kg
0.5 6.52 4.35 142 604 912 B2 500 000
0.8 2830 520 37 116 000 285 000 –
Source: Data derived from United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (1993) Sources and effects of ionizing radiation. UNSCEAR 1993 Report to the General Assembly. Annexure B. New York: United Nations.
B250 EBq of radioactivity released by nuclear weapons testing. For this reason, plutonium nuclides were considered initially to be only a minor hazard; thus far, fewer detailed measurements of 239,240Pu in air or on the earth’s surface have been made compared to other fallout radionuclides, especially 90Sr. The radionuclides injected into the stratosphere were brought down to the earth’s surface in rainfall and other climatic processes, thus contaminating both the surface soils and waters, and leading to measurable concentrations in the surface air in the early years.
Plutonium in the Air Figure 1 shows the average concentrations of airborne Pu measured in New York City, latitude 411 N, and the Isla de Pascua, latitude 271 S, during the period 1954– 78. In both the Northern and Southern hemispheres, the highest air concentrations were observed in 1963. Measurements at five locations in the Northern Hemisphere, ranging from 191 N to 821 N, yielded a mean value of 3375 mBq m3 in 1963 and 0.770.2 mBq m3 in 1975; the corresponding values for four regions in the Southern Hemisphere, ranging from 21 S to 531 S, were 1.971.0 and 0.2702 mBq m3, respectively. From 1967 to 1977, the air concentrations in both hemispheres appeared to be decreasing with a half-life of approximately 4 years. This decrease appeared to continue, and today, except perhaps in areas close to some nuclear installations, concentrations of 239,240Pu in surface air are close to or below the limits of detection. Although the surface air concentrations of 239,240Pu were about two orders of magnitude smaller than the deposition on the soil, airborne fallout 239,240Pu formed an important source of human intake. The airborne 239,240
100 NYC 41 °N Is de Pas 27 °S 10 µBq m−3
high-energy, 4.5–5.5 MeV, a particles, which are potentially highly radiotoxic; for this reason, there has been much public concern about the possible effects on human health if plutonium is released into the environment.
1
0.1 1950
1960
1970
1980
Year
Figure 1 The concentrations of 239,240Pu measured in surface air in the Northern and Southern hemispheres from 1954 to 1977. Data from Fisenne IM, Perry PH, and Chu NY (1983) measured 234,238 U and fallout 239,240Pu in human bone ash from Nepal and Australia: Skeletal alpha dose. Health Physics 44(Suppl.)
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Plutonium: Environmental Pollution and Health Effects
plutonium appears to have been in the form of oxide particles, of which approximately 80% were small enough to be inhaled by humans or animals and deposited deep in the lungs. Surface Deposition Figure 2 illustrates the annual rate of deposition of fallout Pu and 90Sr on surface soil in six cities in Japan (latitude 33–401 N) during the period 1945–97. The data indicate that the fallout deposition of both nuclides in Japan reached a peak in 1963 and thereafter declined steadily until about 1987, when it appeared to reach a more or less constant level. After 1987, the annual deposition of both 90Sr and 239,240Pu became more or less constant, averaging 0.1570.03 and 0.003670.0012 mBq m2, respectively. These very low values suggest that there was no further fallout from the atmosphere and the very low deposition of both nuclides measured on the collectors at this time may well represent material resuspended from the ground. From 1963 to 1985, the decrease in both 90Sr and 239,240Pu depositions approximate to monoexponential functions with half-times of B4–5 years. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) calculated the average values for the global surface distribution of plutonium and americium nuclides listed in Table 3. The highest deposition in each hemisphere was observed in the temperate, 401–501, regions. The total deposition in the 401–501 of the Northern Hemisphere was approximately 3.6 times larger than in the same band in the Southern Hemisphere. Measurements made at some 54 locations across the world on samples of soil collected in the 1970s suggest that the 239,240Pu 239,240
deposition at any individual location might have ranged from B0.1 to 4 times the average value for the relevant hemisphere. In addition to 239,240Pu, nuclear weapons testing also gave rise to a stratospheric inventory of approximately 0.5 PBq of 238Pu; by 1966 this had decreased to approximately 11 TBq. The behavior of this 238Pu would be expected to be similar to that of the fallout 239,240Pu. The 238,239,240Pu deposited on the soil would have been in the form of insoluble high-fired oxides with extremely slow dissolution kinetics; however, in the presence of water, redox and hydrolytic reactions, sorption, and complexation may occur and some of the plutonium will be taken up by vegetation and from thence into grazing animals and the human food chain. With the passage of time, the particles migrate into the deeper layers of the soil. Concentrations in Water In comparison to the deposition on soils, the fallout that fell on the oceans and inland lakes led to 239,240Pu concentrations in water that are about three orders of magnitude lower than those measured in soils, or in marine or lake or river sediments. This is primarily due to the poor solubility of plutonium in the fallout particles and rapid adsorption onto particulate matter in the waters; however, redox, hydrolysis, and other reactions play an important role and in some waters more than 70% of the 238 or 239,240 Pu may be in the Pu(V,VI) oxidation states. Concentrations in the ocean have also increased as a result of discharges of plutonium from nuclear facilities, such as Sellafield in Cumbria, UK and Cap La Hague, France, or from the US Pacific Proving Grounds in the
1000 239,240 90
Bq m−2 per year
100
Pu
Sr
10
1
0.1 0.01
0.001 1940
1950
1960
1970 Year
1980
1990
2000
Figure 2 Deposition of fallout 239,240Pu and 90Sr in Japan during the period 1945–97. The error bars shown represent the standard deviation on the mean values for 239,240Pu. Data recalculated Hirose K, Igarashi Y, Aoyama M, and Miyao T (2001) Long-term trends of plutonium fallout observed in Japan. In: Kudo A (ed.) Plutonium in the Environment. Edited Proceedings of the Second Invited International Symposium. Radioactivity in the Environment Series, Vol. 1, pp. 251–266. Amsterdam: Elsevier, and Hisamatsu S, Takizawa Y, and Abe T (1987) Ingtestion intake of fallout in Japan. Health Physics 52: 193–200.
Plutonium: Environmental Pollution and Health Effects
599
Table 3 Estimated population-averaged deposition densities of 238, 239,240,241Pu, 241Am and 90Sr on surface soils in the Northern and Southern hemispheres Latitude-
RN:90Sr ratio
Population-weighted deposition density (Bq m2) Northern hemisphere
Southern hemisphere
401 –501
01 –901
401 –501
01 –901
World average
1.5 35 23 730 25 3230
0.98 23 15 480 17 2140
0.41 10 6 200 7 890
0.25 6 4 120 4 540
0.90 22 14 440 15 1960
Radionuclide (RN) Plutonium-238 Plutonium-239 Plutonium-240 Plutonium-241 Americium-241 Strontium-90
0.000 46 0.011 0.007 2 0.23 0.007 7 1.00
Source: Data derived from United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (1993) Sources and effects of ionizing radiation. UNSCEAR 1993 Report to the General Assembly. Annexure B. New York: United Nations.
Table 4 Concentrations of 239,240Pu in sea and other waters resulting from fallout from weapons testing or from releases from nuclear installations Location
Nuclear weapons fallout Atlantic Ocean (N þ S) Pacific Ocean (N þ S) Lake Michigan Discharges from nuclear installations Irish Sea – Sellafield at a depth of 21 m (1989–) Irish Sea – Dublin Bay (1989) Mediterranean Sea – Latitudes 37–421 N Norwegian and Greenland seas (1995) Baltic Sea Arctic Ocean
239,240
Pu concentration (mBq m3) 2.5–63 2–16 8–12 B70 000 6173 12–18 8.370.7 (3–38) 4–8 3.771.4
Marshall Islands. Natural water mass circulation may cause some of the plutonium from these discharges to migrate into distant oceans. For example, activity from the 717 TBq of plutonium discharged into the Irish Sea from Sellafield up to 1995 has been detected in the Baltic, Barents, and Arctic seas. In contrast, in the northwest Pacific Ocean, the plutonium profiles and inventories near the Enewetok and Bikini test sites remained unchanged over 24 years. Table 4 illustrates some of the concentrations measured in different water masses. Some of the plutonium in the oceans, rivers, and lakes can be taken up by plankton and other aquatic biota, including fish that may form part of the human food chain. Other Important Releases Plutonium-238 from a failed satellite radioisotope thermoelectric generator (RTG)
Since 1961, the United States has used 238Pu-fueled RTGs in more than 20 satellites and spacecraft. On 21
April 1964, the launch of the Transit 5-BN-3 navigational satellite, fitted with a 238Pu-containing SNAP 9A RTG failed and the device burnt up in the stratosphere over the Indian Ocean, releasing approximately 550 TBq 238 Pu (B80% in the Southern Hemisphere and 20% in the Northern). By the end of 1970, the estimated total stratospheric reservoir had decreased to B37 TBq, consistent with a residence half-time of approximately 1.2 years. This 238Pu, which was largely in the form of insoluble oxides, also contributed to the surface depositions of this nuclide across the world. The Chernobyl accident
On 26 April 1986, during low power engineering tests, one of the reactors at the Chernobyl Nuclear Power Plant, in the Ukraine, which was then part of the FSU, became unstable, causing a thermal explosion and a fire that effectively destroyed the reactor and its building. As a result of this some 5300 PBq of nongaseous and particulate radionuclides, including B6.1 TBq of 238þ239þ240þ241 Pu were released into the atmosphere. These radionuclides formed a plume that was moved by the prevailing winds first to the north and west and then eastwards and around the world, small amounts of radioactivity being detected in Japan and the United States. Deposition was uneven, being influenced by rain and other climatic conditions, and in some areas of the Ukraine, Hungary, Poland, Austria, and Germany, milk and food crops were contaminated to levels that led to their destruction. However, for the plutonium radionuclides, the deposition was small and was generally of no radiological significance. Aircraft accidents Palomares
On 17 January 1966, a US Air Force B52 bomber carrying four thermonuclear bombs collided with a tanker aircraft above the village of Palomares in southeastern Spain.
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Plutonium: Environmental Pollution and Health Effects
Two of the weapons were recovered intact but the conventional explosives in the other two detonated causing weapons-grade plutonium to be spread over the village and the surrounding area, resulting in the contamination of approximately 2.25 km2 of farmland with surface densities of B0.1–1.18 MBq (50–500 mg) 239,240Pu m2. Immediate remedial measures involved the removal to the United States of the top 10 cm of soil from those areas contaminated with 41.18 MBq (500 mg) m2, and the plowing of areas contaminated with 5–500 mg m2 to a depth of 20 cm, and then covering them with new top soil. Daily air sampling in the village and at a site contaminated with B0.1–1.18 MBq (50–500 mg) 239,240Pu m2, during the period from 1966 to 1980, yielded average concentrations of 5.5 and 52 mBq m3, respectively: values that are less than one-tenth of those that would be considered of radiological concern for the general public. Samples of soil collected around Palomares in May 1998 revealed some hot spots at other sites, including the village. The 239,240Pu concentrations were comparable with those expected from fallout 239,240Pu. Thule
In January 1968, another US B52 aircraft carrying four thermonuclear weapons crashed on the 1 m thick sea ice approximately 12 km from the Thule Air Base in NW Greenland. The conventional explosive in all four weapons detonated and the full load of aviation fuel caught fire resulting in the dispersal of oxidized plutonium. The visibly blackened area had a density of B2.2 MBq 239,240Pu m2 and the total deposition was approximately 7 PBq 239Pu. Some parts of the aircraft broke through the ice, contaminating the marine environment in the 180–230 m deep Bylot Sound. The contaminated ice and the remaining wreckage of the plane were collected and returned to the United States for disposal. It was estimated that in 1968 the seabed of the Bylot Sound was contaminated with B1.4 TBq 239,240Pu, 0.025 TBq 238Pu, 4.6 TBq 241Pu, and 0.07 TBq 241Am. Since 1966, the radioactivity in the sediments, water, and biota in this region has been widely studied. In 1997, 239,240 Pu concentrations in the top 0–3 cm of sediment were still high (B600 Bq kg1 dry weight) in the sediments immediately under the accident site, but were 10–20 times lower in the remaining deep areas of Bylot Sound. Concentrations of 239,240Pu in edible biota such as squid, fish, and shrimp were one to two orders of magnitude less than those in the sediments. Seawater concentrations in the Bylot Sound were in the range 5–10 mBq 239,240Pu m3. Rocky Flats Nuclear Weapons Plant
Two major fires have occurred at the Rocky Flats Nuclear Weapons Plant, which is situated approximately
25 km from Denver, Colorado. In the first in 1957 spontaneous ignition of 15–20 kg plutonium caused contamination in the plant area. In the second fire in 1969 several kg of plutonium metal combusted spontaneously causing a smoke plume that spread to surrounding areas; releasing B130 GBq, much of it spreading outside the site boundaries. Soil densities of up to 50–70 Bq Pu m2 were found at or beyond the plant perimeter. The Mayak Production Association
Since 1948 this complex, situated in the southern Urals near the town of Kyshtym, Russia and 150 km from Chelyabinsk, has operated seven nuclear reactors and two reprocessing plants and has discharged B100 PBq of fission products, including at least 40 TBq of plutonium, into the Techa River. These discharges, plus the explosion of a large chemical tank in 1957, caused widespread contamination both of the local environment and of some thousands of people. Tomsk, Russian Federation
A further release of some 300 kg of plutonium as a result of the explosion of a tank containing kerosene and tributylphosphate occurred at Tomsk in Siberia in 1993, causing widespread contamination over an area of 120 km2. The Semipalatinsk Nuclear Testing Site
This site, situated in NE Kazakhstan was involved with 86 atmospheric, 30 surface, and 346 underground nuclear tests between 1949 and 1989. Core samples 23 cm in depth indicated depositions of 330 kBq m2 near the hypocenter of the first nuclear test and 1–4 kBq m2 at 5–15 km from ground zero. Measurements in October 2005 within the inhabited village of Dolon, 80 km northeast of the boundary of the test area, showed deposition densities ranging from 0.076 to 40.9 kBq m2 with an average of 6 kBq m2.
Movement of Plutonium from Surface and Sediment Deposits Chemically, plutonium in the fallout from weapons testing was almost all in the form of oxides formed at high temperatures and in the form of small particles. The largely insoluble, plutonium particles deposited on soil surfaces appear to be migrating slowly to depths of up to approximately 40 cm; similar migration is also found in marine and freshwater sediments. Plutonium may be incorporated into plants by direct foliar deposition from the air, either as material carried down in rainfall, or as fine soil particles resuspended by wind and rain with subsequent deposition on the plant. Foliar absorption of the deposited plutonium or uptake from the soil through
Plutonium: Environmental Pollution and Health Effects
the roots may occur; however, in general these processes play minor roles and the major contamination of grassland and leafy food crops comes from foliar deposition of resuspended material. Radionuclide uptake by plants, or other biota, is often expressed as a concentration ratio (CR), defined as the radioactivity per kg dry weight of plant or other material expressed as a fraction of the radioactivity per kg dry weight of soil, per liter of water. Values of CR have been obtained mainly by greenhouse or field studies with quite highly contaminated soils, for example, in the vicinity of reprocessing or other nuclear plants; similarly CR for aquatic species have been obtained from studies in rivers or oceans receiving plutonium discharges from such installations. Direct measurement of CR by studies with biota grown on soils, or in waters, contaminated only by fallout plutonium are often impracticable because the concentrations are near to or below the limits of detection of the analytical method. The data suggest that for natural vegetation, including pastures and leafy vegetables, the CR may range from B0.02 to 0.6, and for cereals, fruits, and root vegetables from 0.0001 to 0.3. For animal products, CRs are much smaller ranging from B2 108 to 1 107 for the transfer from soil, via feed, to eggs, beef, lamb, and lamb or beef liver. Plutonium deposited in the oceans, rivers, and lakes can be taken up by plankton and shellfish and fish that may form part of the human food chain. Table 5 shows the concentrations of 238Pu and 239,240Pu measured in fish muscle collected from the Baltic Sea, which is contaminated by both fallout and Chernobyl-derived plutonium plus a small input from Sellafield discharges. The table also shows the concentrations found in winkles and mussels collected off the coast of Cumbria, UK near the Sellafield reprocessing plant. Table 5 shows that, although concentrations in the commonly eaten fish from the Baltic Sea are o1 mBq kg1, those in the shellfish from the much more highly contaminated waters off Sellafield are three orders of magnitude greater.
Table 5 Concentrations of 238Pu, edible parts of fish and shellfish Species
Location
239,240
Pu observed in the
Concentration (mBq kg1) 238
239,240
0.036
0.13
0.13 0.09 0.027 7000– 27 000 7000– 13 000
0.24 0.29 0.16 31 000– 113 000 31 000– 46 000
Pu
Flounder (muscle) Herring (muscle) Cod (muscle) Sprat (muscle) Winkles Mussels
Gdansk Bay (Baltic)
Sellafield (Irish Sea)
Pu
601
Human Exposure to Environmental Plutonium Plutonium can enter the human body by inhalation of contaminated air or by ingestion of contaminated foods or drinking water. The fractional absorption of plutonium from the human gastrointestinal tract is very low, (B1–10) 104 of the ingested activity. The relative intakes by inhalation and ingestion by residents of Finland during the period of high fallout, from 1954 to 1978, are illustrated in Figure 3; in this figure, the intake by ingestion is shown as both the total estimated intake into the alimentary tract and the amounts entering the bloodstream assuming a fractional absorption of 5 104. This figure indicates that inhalation represented the major route of intake with the amounts of 239,240Pu inhaled by the southern Finns and Lapps being broadly similar. Since the air concentrations in Finland were comparable with those recorded for other places in the Northern Hemisphere, this inhalation intake may be regarded as reasonably typical for this hemisphere during this period. In contrast, the amounts ingested by the Lapps were 10–15 times greater than those of the southern Finns; this is due to the very high proportion of reindeer liver and meat in the Lapp’s diet. Reindeer feed on lichens that take up much higher amounts of 239,240Pu than other types of pasture; reindeer liver that constitutes B70% of the Lapps diet, contained up to 400 mBq 239,240 Pu kg1 with much lower concentrations in the meat B5 mBq 239,240Pu kg1. After 1973, the annual ingestion by both groups remained essentially constant. Of the inhaled plutonium, depending on the chemical form of the inhaled material, some will be relatively rapidly cleared from the respiratory tract and swallowed, some will penetrate deep into the lung from where some may be absorbed into the blood, and another fraction may migrate into the alveolar macrophages where it will remain for long periods. The plutonium that is absorbed into the blood, either from the alimentary tract or from the lungs, will deposit mainly in the liver and bone, where it is retained for long periods. The organ distribution of fallout plutonium in the human body can be seen in Figure 4, which shows the median 239,240Pu content of the liver, bone, lungs þ tracheobronchial lymph nodes (TBLN), and the estimated total body content of adult persons who died between 1970 and 1982 in several countries; all of whom had lived throughout the period of maximum fallout activity between 1963 and 1973. The data in Figure 4 suggest that the highest values, B150 mBq, were seen in persons who died in the United States or Japan during the period 1970–75; by the early 1980s, the values appear to have decreased to approximately 50–120 mBq. Calculations suggest that persons born in 1970, or later, will have much smaller body contents of fallout 239,240Pu, o3 mBq; however, such levels
602
Plutonium: Environmental Pollution and Health Effects
10 000
Inhalation S Finns
Inhalation Lapps
Total ingestion S Finns
Total ingestion Lapps
Ingestion to blood S Finns
Ingestion to blood Lapps
1000
Annual intake (mBq a−1)
100
10
1
0.1
0.01
0.001 1955
1960
1965
1970
1975
1980
Years
Figure 3 Estimated annual intake of 239,240Pu by Lapps and residents of Southern Finland during the period 1955–78. The intake by ingestion is shown as total ingestion into the alimentary tract, and as the amount absorbed into the blood stream assuming a fractional absorption of 0.0005. Data recalculated from that of Mussalo-Rauhamaa H (1981) Accumulation of plutonium from fallout in southern Finns and Lapps. Report Series Radiochemistry 4, University of Helsinki. Total body/organ content (mBq) 0
30
60
90
120
150
180
210
Japan, Tokyo, 1970 Japan, Niagata, 1984 USA − 5 States, 1970 USA − 5 States, 1977 USA, New York City, 1974 USA, Washington State, 1970−5 UK (excl. W.Cumbria), 1980−84 UK − W.Cumbria, 1980−84 Finland, Lapps, 1976−79 Other tissues Finland, south, 1976−79
Lung+TBLN Liver
Germany, Munich, 1980−81
Bone
Figure 4 The comparative body contents of 239,240Pu in the bones, liver, lungs þ tracheobronchial lymph nodes, other tissues, and total body content of persons who died in various parts of the world between 1970 and 1984. The total height of each column represents the total body content of the individuals in that group.
Plutonium: Environmental Pollution and Health Effects
are difficult to confirm by measurements of autopsy samples, even with the most sensitive methods of analysis that have a detection limit of B0.5 mBq per sample. For radiological protection purposes, the International Commission on Radiological Protection (ICRP) assumes that of the plutonium that enters the blood, 30% will be deposited in the liver and be retained with a half-time of 20 years; a further 50% will deposit in bone and be retained with a half-time of 50 years; the remaining 20% is deposited in the other tissues or excreted. Analysis of the data shown in Figure 4 indicates that the observed median liver and skeleton concentrations account for 37% and 53%, respectively, of the estimated total body content. Individual values ranged from 15% to 66% for liver and 26% to 75% for the skeleton. The data for the years 1970 and 1977 for six states in the United States indicate that the median total body content was decreasing over this time with a biological half-time of B6 years, suggesting that the retention in the body may be less prolonged than that proposed by ICRP. The information on the levels of environmental 238Pu in the human body is sparse, as the concentrations in tissues other than bone are often below the limits of detection of the best available analytical methods. Assuming that the 238Pu content of the skeleton is 60% of the total body content, the measurements on a few persons who died in Colorado or Washington, DC during the period 1977–79, suggest a total body content of B18 mBq, or about one-fifth of that of 239,240Pu. The data for the few residents of west Cumbria, near the Sellafield facility, suggest body contents of approximately 50% higher than those found in the other parts of the United Kingdom. For some people in this area, their plutonium intake is increased by the consumption of locally harvested shellfish (winkle and mussels) and this increases the annual radiation dose they receive from all other environmental sources, B2.6 mSv, by B20 mSv. In some areas, the Chernobyl accident led to further intake of plutonium; for example, estimates for the Bialystok region of Poland suggest that the 239,240Pu body content may have increased by B6 mBq, an increase of approximately 8% over that expected from weapons fallout alone. Studies of persons dying after living for B25 years at up to 8 km from the Mayak complex suggest plutonium body burdens of B3–6 Bq, more than an order of magnitude greater than that expected from fallout plutonium alone.
Potential Health Effects of Environmental Plutonium The high specific activities of 238Pu and 239Pu, 634 kBq mg1 (1.5 pg Bq1) and 2.3 kBq mg1 (434 pg Bq1), respectively, mean that radiotoxic effects will predominate
603
over any chemical toxicity. There is, fortunately, little direct information on the radiotoxicity of 238,239Pu in humans and most of the available information comes from studies of exposed workers, who were often also exposed to g rays or other forms of radiation. Studies of the radiotoxicity of 239Pu in experimental animals have demonstrated that inhalation of large activities of either 238Pu or 239Pu can cause acute effects such as radiation pneumonitis, pulmonary fibrosis, bone changes (osteodystrophy), and blood and liver abnormalities. In addition, at lower activities tumors of bone, lung, and liver may arise after latent periods of a few to more than 10 years. There are some differences in the effects of inhaled 238PuO2 and 239PuO2, which result from differences in their biokinetics and radiation dose patterns, which make 238Pu somewhat more mobile than 239Pu. Inhaled plutonium may remain in the lungs or migrate to the bones, liver, or other body organs. Following ingestion of plutonium o0.1% will be absorbed into the bloodstream from where it will be deposited predominantly in the liver and skeleton. Plutonium deposited in liver and bone appears to remain in the body for many years; the fallout data discussed earlier suggest that between 1970 and 1980, the total body content of 239,240 Pu decreased with a half-time of B6 or more years; however, studies in experimental animals intravenously injected with 239Pu suggest biological half-times of up to 40 or more years. The radiotoxicity studies in animals have generally been conducted with activities that were much higher than those encountered by workers, and orders of magnitude greater than those accumulated by members of the general public from the inhalation or ingestion of environmental plutonium. Epidemiological studies, involving 18 833 persons (14 075 males and 4758 females) who worked at the Mayak Production Association from 1948 to 1972 and who were followed up to December 2000, found that 121 cases of pulmonary fibrosis (pneumosclerosis) (65 males and 56 females) had arisen in persons exposed to an average lung dose from plutonium of 4.070.5. Gy plus 0.9370.14 Gy of external g radiation. In addition, 592 lung cancer deaths (532 males and 60 females) were recorded in this period; the data suggesting that a statistically significant, dose-dependent increase in lung cancer mortality was seen with committed effective doses to the respiratory tract Z6.2 Sv. Compared with global environmental levels, these workers inhaled very large amounts of plutonium. The ongoing studies of the Mayak populations appear to provide powerful evidence that plutonium was the most likely cause of some other types of cancer. Long-term medical follow-up of 26 Manhattan project workers with residual body contents of 52–3180 Bq
Plutonium: Environmental Pollution and Health Effects
(median 500 Bq) 239Pu dating from 1944 to 1945 showed some evidence for a preferential reduction in suppressor T-lymphocytes, indicating some potential effects on the immune system; however, the frequency of these aberrations could not be correlated with their plutonium body contents. By the end of 1994, 7 of these 26 workers had died, compared with an expected 13 deaths based on the mortality rates for white males in the general US population. Of the seven deaths, one was accidental, two due to cardiovascular disease, and one due to pneumonia; the remaining three were due to prostate, lung, and bone cancers in subjects with 239Pu body contents of 740, 3080, and 580 Bq, respectively. Among the 19 workers still alive at the end of 1990, three, aged 75–81 years, had been diagnosed with prostate cancer. Based on the age-adjusted incidence rates for prostate cancer in the US white males, the standardized incidence ratio (SIR) for the four cases in this group is 1.8 (95% confidence limits (CL) 0.5–4.6), because the wide 95% CL includes an SIR, the incidence of prostate cancer cannot be regarded as significantly different from that which would have been expected in a nonexposed group of this small size. A total of three lung cancers were found in these 26 workers over the 50 year observation period, the age-adjusted SIR is 1.8 (95% CL 0.4–5.2), which again suggests that the incidence of lung cancer was not significantly increased. The occurrence of the single case of osteosarcoma of the sacrum in the Los Alamos worker group is noteworthy since the animal studies have clearly demonstrated the induction of bone cancers by 239Pu. The presence of this tumor in this small study group is statistically significant when compared with the mortality rates for white US males, or with a group of 876 unexposed Los Alamos workers. However, when this case was included in a larger study involving 3775 plutonium-monitored males who worked at Los Alamos from 1943 to 1977, of whom 303 were exposed with estimated body contents Z74 Bq 239 Pu, it was found that the incidence rate ratios were not significantly different from 1 for bone or any other form of cancer. No bone cancers have been reported among the 5143 plutonium-exposed Rocky Flats workers studied. Neither the epidemiological studies of the Los Alamos or the Rocky Flats workers nor the animal studies identify any minimum levels of plutonium in the human body, or in air, food, or water, which would likely lead to harmful effects. However, for radiological protection purposes, the ICRP recommends adoption of the socalled linear-no-threshold model for the induction of cancers by radiation; this conservative hypothesis assumes that any amount of absorbed radiation, no matter how small, may cause some damage. However, at present there is no good evidence to confirm that this hypothesis holds for the very low radiation doses, generally o10 mSv, likely to be received by workers in
well-regulated workplaces, or by the general public from plutonium released into the environment. Any consideration of the potential health effects of environmental plutonium must also take into account the amounts of the natural a-particle emitting radionuclides that are also inescapably present in the human body, especially those that deposit preferentially in bone (e.g., 238U and 228,230,232Th). Figure 5 compares the total body, liver, and lung contents of 238þ239þ240Pu with those for 234þ235þ238U, and 228þ230þ232Th in the US residents of Colorado who died during 1977–79. Calculation of the total radiation doses delivered by the isotopes deposited in bone, the major tissue of radiological concern, yields dose rates of B2 mSv a1 for the uranium isotopes and B16 mSv a1 for the thorium isotopes and their radioactive daughter products, but only B0.3 mSv a1 for 238þ239þ240Pu. These are very small radiation doses. Assuming the ICRP risk factor for an irradiation-induced cancer of 0.01 Sv1, and an exposure to 10 mSv from plutonium might cause 1 in 10 million chance of inducing a bone tumor: this is about 100 000-fold smaller than the risk of developing a spontaneous (natural) bone tumor. Such a low risk could not be detected by any currently available method and would be considered by most people to be negligible. Thus, it appears very unlikely that the levels of 238Pu and 239,240 Pu currently present in the environment will pose any significant threat to human health. A potential cause for concern is the B1200 tonnes of, now largely unwanted, plutonium that has arisen from the decommissioning of nuclear weapons and from nuclear power production. If even a few kilograms of this plutonium were to fall into the hands of terrorists and be released as a fine aerosol into a crowded building or stadium, this could lead to hundreds, even thousands,
600 Bone Other tissues Liver Lung+TBLN
500 Organ content (mBq)
604
400
300
200
100
0 234+235+238
U
228+230+232
Th
238+239+240
Pu
The comparative body contents of 228þ230þ232Th, U, and 238þ239þ240Pu in the bodies of persons who died in Colorado during the period 1977–79.
Figure 5
234þ235þ238
Plutonium: Environmental Pollution and Health Effects
of persons inhaling sufficient activity to cause serious harm within either a relatively short or a very long period. However, assuming that this largely unwanted plutonium can be securely stored, or burnt up in nuclear power reactors (a process that should not increase environmental exposure), and that there is no future nuclear arms race with atmospheric or near surface weapons testing, plutonium in the global environment should pose no future hazard to members of the public. See also: Clinical Consequences of Radiation Exposure, Ionizing Radiation Exposure: Psychological and Mental Health Aspects, Risk to Populations Exposed from Atmospheric Testing and Those Residing Near Nuclear Facilities.
Further Reading Choppin GR, Liljenzin LO, and Rydberg J (1995) Radiochemistry and Nuclear Chemistry. Oxford: Butterworth-Heinemann. Harley JH (1980) Plutonium in the environment: A review. Journal of Radiation Research (Japan) 21: 83--104. International Commission on Radiological Protection (ICRP) (1986) The metabolism of plutonium and related elements. ICRP Publication 48. Annals of the ICRP 16(2/3).
605
International Commission on Radiological Protection (ICRP) (2008) Recommendations of the ICRP. ICRP Publication 103. Annals of the ICRP 37(2–4). Kudo A (ed.) (2001) Plutonium in the Environment. Edited Proceedings of the Second Invited International Symposium. Radioactivity in the Environment Series, Volume 1. Elsevier: Amsterdam. Mussalo-Rauhamaa H. (1981) Accumulation of plutonium from fallout in southern Finns and Lapps. Report Series in Radiochemistry 4. University of Helsinki National Council on Radiation Protection and Measurement (NCRP) (2001) Scientific Basis for evaluating the risks to populations from space applications of plutonium. NCRP Report No. 131. Bethesda MD: NCRP. Taylor DM (1995) Environmental plutonium in humans. Applied Radiation and Isotopes 46: 1245--1252. Taylor DM (2002) Radionuclides in the environment. In: Sarkar B (ed.) Heavy Metals in the Environment, pp. 95--120. New York: Marcel Decker. Taylor DM and Taylor SK (1997) Environmental uranium and human health. Reviews of Environmental Health 12: 147--157. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (1993) Sources and effects of ionizing radiation. UNSCEAR 1993 Report to the General Assembly, with Annexes. New York: United Nations. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (2000) Sources and effects of ionizing radiation. UNSCEAR 2000 Report to the General Assembly, with Annexes. Annex J. Exposures and effects of the Chernobyl accident. New York: United Nations.
Abbreviations CL CR FSU ICRP
confidence limit concentration ratio former Soviet Union International Commission on Radiological Protection radioisotope thermoelectric generator standardized incidence ratio United Nations Scientific Committee of the Effects of Atomic Radiation
RTG SIR UNSCEAR
Introduction Plutonium, Element 94, was a primeval element, with gigatonnes of 244Pu and 239Pu being produced by supernova explosions during the creation of the universe and at the genesis of the earth; at that time, their concentration in the earth’s crust was likely to have been of the order of mg kg1. Indeed, 244Pu and 239Pu can be considered to be the parent nuclides of the natural thorium and actinium series, respectively. Since all plutonium isotopes are radioactive (Table 1) with physical half-lives (Tp) that are short in relation to the age of the earth, essentially all the cosmogenic plutonium has now been lost by radioactive decay. It has been estimated that the concentrations of 244Pu in the earth’s crust might be 3 1022 g kg1. However, since the formation of the Table 1
earth, up to B30 kg 239Pu a1 has been produced from 238 U by the spontaneous neutron-capture reaction: 238
b
Uðn;gÞ 239 U -
239
23 min
b
Np -
2:3 d:
239
Pu:
Today the tiny concentrations of 239Pu – B2.1014 g kg1 in the earth’s crust (B80 amol Pu kg1 or B50 mBq 239Pu kg1) – formed through the above reactions, are virtually the only naturally produced plutonium in the environment. The majority of the plutonium currently found in the global environment has arisen since 1945 as the result of human activities, predominantly the development, manufacture, and atmospheric testing of nuclear weapons – by the United States of America, the Former Soviet Union, the United Kingdom, France, and the Peoples Republic of China. Nuclear power production and fuel processing, nuclear waste disposal, and mishaps in nuclear facilities (e.g., the accident at the Chernobyl Nuclear Power Plant in 1986) also made further contributions, but generally on a local rather than a global scale. Another isotope 238Pu has found quite wide application in radioisotope thermoelectric generators (RTG), especially for spacecraft. The burn-up of a 238Pucontaining RTG in the stratosphere above the Indian Ocean, following a failed satellite launch in 1964, caused further worldwide contamination. The plutonium isotopes of greatest environmental interest, 238Pu and 239Pu, decay with the emission of
Some properties of the principal isotopes of plutonium
Nuclide
Half-life (years)
Decay modea (MeV) (% decays)
Specific activity (Bq g1)
Environmental oxidation stateb
Plutonium-238
87.7
6.34 10þ11
IV, V
Plutonium-239
2.4 10þ4
2.30 10þ09
IV, V
Plutonium-240
6563
8.40 10þ09
IV, V
Plutonium-241
14.4
3.81 10þ12
IV, V
Plutonium-244
8.2 10þ7
2.30 10þ6
IV, V
Americium-241
432.7
a 5.456 (28) a 5.499 (72) a 5.105 (12) a 5.143 (15) a 5.156 (73) a 5.124 (27) a 5.168 (73) a 4.897 (0.002) b 0.021 (100) a 4.589 (99.9) SF 0.1% a 5.388 (1) a 5.443 (13) a 5.486 (85)
1.27 10þ11
III
Principal decay mode (low-energy g-ray emission and the fractions of spontaneous fission (SF) of o 0.01% have been ignored). The main oxidation state in soils vegetation and animals, including humans is likely to be IV, but V has been reported in some waters.
a
b
596
597
Plutonium: Environmental Pollution and Health Effects
The Distribution and Concentrations of Plutonium in the Environment The available data do not provide a very comprehensive picture of the current levels of plutonium contamination in all parts of the world. It should be recognized that the methods for the determination of plutonium radioactivity are extremely sensitive and some of the concentrations presented in the following text may be orders of magnitude below those that might give concern about human or environmental health. The Global Fallout from Nuclear Weapons Testing The explosion of the second atomic bomb, Fat Boy, above Nagasaki on 9th August 1945 began the widespread release of plutonium into the atmosphere, but by far the largest contribution came from the atmospheric testing of more than 500 atomic and thermonuclear weapons between then and the end of the 1970s. The fallout from such weapons amounted to a total of B250 EBq (2.5 10þ20 Bq) and contained a broad spectrum of radionuclides with half-lives ranging from a few days, 131 I, to many years, including 90Sr, 137Cs and 238Pu, 239Pu, 240 Pu and 241Pu. In the next half-century, most of the shorter-lived radionuclides decayed, leaving only 90Sr and 137Cs, and the plutonium isotopes, as the major fallout nuclides. The amounts of these nuclides dispersed in the atmosphere as a result of nuclear weapons testing are shown in Table 2. The data in Table 2 indicate that the release of a total of B11.5 PBq (1.1 1016 Bq) of 238,239,240 Pu represented only a tiny fraction of the total of Table 2 The amounts of plutonium and some other radionuclides released into the atmosphere by nuclear weapons testing Radionuclide
Plutonium-238 Plutonium-239 Plutonium-240 Plutonium-241 Strontium-90 Caesium-137 Other radionuclides
Estimated release PBq (10þ15Bq)
kg
0.5 6.52 4.35 142 604 912 B2 500 000
0.8 2830 520 37 116 000 285 000 –
Source: Data derived from United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (1993) Sources and effects of ionizing radiation. UNSCEAR 1993 Report to the General Assembly. Annexure B. New York: United Nations.
B250 EBq of radioactivity released by nuclear weapons testing. For this reason, plutonium nuclides were considered initially to be only a minor hazard; thus far, fewer detailed measurements of 239,240Pu in air or on the earth’s surface have been made compared to other fallout radionuclides, especially 90Sr. The radionuclides injected into the stratosphere were brought down to the earth’s surface in rainfall and other climatic processes, thus contaminating both the surface soils and waters, and leading to measurable concentrations in the surface air in the early years.
Plutonium in the Air Figure 1 shows the average concentrations of airborne Pu measured in New York City, latitude 411 N, and the Isla de Pascua, latitude 271 S, during the period 1954– 78. In both the Northern and Southern hemispheres, the highest air concentrations were observed in 1963. Measurements at five locations in the Northern Hemisphere, ranging from 191 N to 821 N, yielded a mean value of 3375 mBq m3 in 1963 and 0.770.2 mBq m3 in 1975; the corresponding values for four regions in the Southern Hemisphere, ranging from 21 S to 531 S, were 1.971.0 and 0.2702 mBq m3, respectively. From 1967 to 1977, the air concentrations in both hemispheres appeared to be decreasing with a half-life of approximately 4 years. This decrease appeared to continue, and today, except perhaps in areas close to some nuclear installations, concentrations of 239,240Pu in surface air are close to or below the limits of detection. Although the surface air concentrations of 239,240Pu were about two orders of magnitude smaller than the deposition on the soil, airborne fallout 239,240Pu formed an important source of human intake. The airborne 239,240
100 NYC 41 °N Is de Pas 27 °S 10 µBq m−3
high-energy, 4.5–5.5 MeV, a particles, which are potentially highly radiotoxic; for this reason, there has been much public concern about the possible effects on human health if plutonium is released into the environment.
1
0.1 1950
1960
1970
1980
Year
Figure 1 The concentrations of 239,240Pu measured in surface air in the Northern and Southern hemispheres from 1954 to 1977. Data from Fisenne IM, Perry PH, and Chu NY (1983) measured 234,238 U and fallout 239,240Pu in human bone ash from Nepal and Australia: Skeletal alpha dose. Health Physics 44(Suppl.)
598
Plutonium: Environmental Pollution and Health Effects
plutonium appears to have been in the form of oxide particles, of which approximately 80% were small enough to be inhaled by humans or animals and deposited deep in the lungs. Surface Deposition Figure 2 illustrates the annual rate of deposition of fallout Pu and 90Sr on surface soil in six cities in Japan (latitude 33–401 N) during the period 1945–97. The data indicate that the fallout deposition of both nuclides in Japan reached a peak in 1963 and thereafter declined steadily until about 1987, when it appeared to reach a more or less constant level. After 1987, the annual deposition of both 90Sr and 239,240Pu became more or less constant, averaging 0.1570.03 and 0.003670.0012 mBq m2, respectively. These very low values suggest that there was no further fallout from the atmosphere and the very low deposition of both nuclides measured on the collectors at this time may well represent material resuspended from the ground. From 1963 to 1985, the decrease in both 90Sr and 239,240Pu depositions approximate to monoexponential functions with half-times of B4–5 years. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) calculated the average values for the global surface distribution of plutonium and americium nuclides listed in Table 3. The highest deposition in each hemisphere was observed in the temperate, 401–501, regions. The total deposition in the 401–501 of the Northern Hemisphere was approximately 3.6 times larger than in the same band in the Southern Hemisphere. Measurements made at some 54 locations across the world on samples of soil collected in the 1970s suggest that the 239,240Pu 239,240
deposition at any individual location might have ranged from B0.1 to 4 times the average value for the relevant hemisphere. In addition to 239,240Pu, nuclear weapons testing also gave rise to a stratospheric inventory of approximately 0.5 PBq of 238Pu; by 1966 this had decreased to approximately 11 TBq. The behavior of this 238Pu would be expected to be similar to that of the fallout 239,240Pu. The 238,239,240Pu deposited on the soil would have been in the form of insoluble high-fired oxides with extremely slow dissolution kinetics; however, in the presence of water, redox and hydrolytic reactions, sorption, and complexation may occur and some of the plutonium will be taken up by vegetation and from thence into grazing animals and the human food chain. With the passage of time, the particles migrate into the deeper layers of the soil. Concentrations in Water In comparison to the deposition on soils, the fallout that fell on the oceans and inland lakes led to 239,240Pu concentrations in water that are about three orders of magnitude lower than those measured in soils, or in marine or lake or river sediments. This is primarily due to the poor solubility of plutonium in the fallout particles and rapid adsorption onto particulate matter in the waters; however, redox, hydrolysis, and other reactions play an important role and in some waters more than 70% of the 238 or 239,240 Pu may be in the Pu(V,VI) oxidation states. Concentrations in the ocean have also increased as a result of discharges of plutonium from nuclear facilities, such as Sellafield in Cumbria, UK and Cap La Hague, France, or from the US Pacific Proving Grounds in the
1000 239,240 90
Bq m−2 per year
100
Pu
Sr
10
1
0.1 0.01
0.001 1940
1950
1960
1970 Year
1980
1990
2000
Figure 2 Deposition of fallout 239,240Pu and 90Sr in Japan during the period 1945–97. The error bars shown represent the standard deviation on the mean values for 239,240Pu. Data recalculated Hirose K, Igarashi Y, Aoyama M, and Miyao T (2001) Long-term trends of plutonium fallout observed in Japan. In: Kudo A (ed.) Plutonium in the Environment. Edited Proceedings of the Second Invited International Symposium. Radioactivity in the Environment Series, Vol. 1, pp. 251–266. Amsterdam: Elsevier, and Hisamatsu S, Takizawa Y, and Abe T (1987) Ingtestion intake of fallout in Japan. Health Physics 52: 193–200.
Plutonium: Environmental Pollution and Health Effects
599
Table 3 Estimated population-averaged deposition densities of 238, 239,240,241Pu, 241Am and 90Sr on surface soils in the Northern and Southern hemispheres Latitude-
RN:90Sr ratio
Population-weighted deposition density (Bq m2) Northern hemisphere
Southern hemisphere
401 –501
01 –901
401 –501
01 –901
World average
1.5 35 23 730 25 3230
0.98 23 15 480 17 2140
0.41 10 6 200 7 890
0.25 6 4 120 4 540
0.90 22 14 440 15 1960
Radionuclide (RN) Plutonium-238 Plutonium-239 Plutonium-240 Plutonium-241 Americium-241 Strontium-90
0.000 46 0.011 0.007 2 0.23 0.007 7 1.00
Source: Data derived from United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (1993) Sources and effects of ionizing radiation. UNSCEAR 1993 Report to the General Assembly. Annexure B. New York: United Nations.
Table 4 Concentrations of 239,240Pu in sea and other waters resulting from fallout from weapons testing or from releases from nuclear installations Location
Nuclear weapons fallout Atlantic Ocean (N þ S) Pacific Ocean (N þ S) Lake Michigan Discharges from nuclear installations Irish Sea – Sellafield at a depth of 21 m (1989–) Irish Sea – Dublin Bay (1989) Mediterranean Sea – Latitudes 37–421 N Norwegian and Greenland seas (1995) Baltic Sea Arctic Ocean
239,240
Pu concentration (mBq m3) 2.5–63 2–16 8–12 B70 000 6173 12–18 8.370.7 (3–38) 4–8 3.771.4
Marshall Islands. Natural water mass circulation may cause some of the plutonium from these discharges to migrate into distant oceans. For example, activity from the 717 TBq of plutonium discharged into the Irish Sea from Sellafield up to 1995 has been detected in the Baltic, Barents, and Arctic seas. In contrast, in the northwest Pacific Ocean, the plutonium profiles and inventories near the Enewetok and Bikini test sites remained unchanged over 24 years. Table 4 illustrates some of the concentrations measured in different water masses. Some of the plutonium in the oceans, rivers, and lakes can be taken up by plankton and other aquatic biota, including fish that may form part of the human food chain. Other Important Releases Plutonium-238 from a failed satellite radioisotope thermoelectric generator (RTG)
Since 1961, the United States has used 238Pu-fueled RTGs in more than 20 satellites and spacecraft. On 21
April 1964, the launch of the Transit 5-BN-3 navigational satellite, fitted with a 238Pu-containing SNAP 9A RTG failed and the device burnt up in the stratosphere over the Indian Ocean, releasing approximately 550 TBq 238 Pu (B80% in the Southern Hemisphere and 20% in the Northern). By the end of 1970, the estimated total stratospheric reservoir had decreased to B37 TBq, consistent with a residence half-time of approximately 1.2 years. This 238Pu, which was largely in the form of insoluble oxides, also contributed to the surface depositions of this nuclide across the world. The Chernobyl accident
On 26 April 1986, during low power engineering tests, one of the reactors at the Chernobyl Nuclear Power Plant, in the Ukraine, which was then part of the FSU, became unstable, causing a thermal explosion and a fire that effectively destroyed the reactor and its building. As a result of this some 5300 PBq of nongaseous and particulate radionuclides, including B6.1 TBq of 238þ239þ240þ241 Pu were released into the atmosphere. These radionuclides formed a plume that was moved by the prevailing winds first to the north and west and then eastwards and around the world, small amounts of radioactivity being detected in Japan and the United States. Deposition was uneven, being influenced by rain and other climatic conditions, and in some areas of the Ukraine, Hungary, Poland, Austria, and Germany, milk and food crops were contaminated to levels that led to their destruction. However, for the plutonium radionuclides, the deposition was small and was generally of no radiological significance. Aircraft accidents Palomares
On 17 January 1966, a US Air Force B52 bomber carrying four thermonuclear bombs collided with a tanker aircraft above the village of Palomares in southeastern Spain.
600
Plutonium: Environmental Pollution and Health Effects
Two of the weapons were recovered intact but the conventional explosives in the other two detonated causing weapons-grade plutonium to be spread over the village and the surrounding area, resulting in the contamination of approximately 2.25 km2 of farmland with surface densities of B0.1–1.18 MBq (50–500 mg) 239,240Pu m2. Immediate remedial measures involved the removal to the United States of the top 10 cm of soil from those areas contaminated with 41.18 MBq (500 mg) m2, and the plowing of areas contaminated with 5–500 mg m2 to a depth of 20 cm, and then covering them with new top soil. Daily air sampling in the village and at a site contaminated with B0.1–1.18 MBq (50–500 mg) 239,240Pu m2, during the period from 1966 to 1980, yielded average concentrations of 5.5 and 52 mBq m3, respectively: values that are less than one-tenth of those that would be considered of radiological concern for the general public. Samples of soil collected around Palomares in May 1998 revealed some hot spots at other sites, including the village. The 239,240Pu concentrations were comparable with those expected from fallout 239,240Pu. Thule
In January 1968, another US B52 aircraft carrying four thermonuclear weapons crashed on the 1 m thick sea ice approximately 12 km from the Thule Air Base in NW Greenland. The conventional explosive in all four weapons detonated and the full load of aviation fuel caught fire resulting in the dispersal of oxidized plutonium. The visibly blackened area had a density of B2.2 MBq 239,240Pu m2 and the total deposition was approximately 7 PBq 239Pu. Some parts of the aircraft broke through the ice, contaminating the marine environment in the 180–230 m deep Bylot Sound. The contaminated ice and the remaining wreckage of the plane were collected and returned to the United States for disposal. It was estimated that in 1968 the seabed of the Bylot Sound was contaminated with B1.4 TBq 239,240Pu, 0.025 TBq 238Pu, 4.6 TBq 241Pu, and 0.07 TBq 241Am. Since 1966, the radioactivity in the sediments, water, and biota in this region has been widely studied. In 1997, 239,240 Pu concentrations in the top 0–3 cm of sediment were still high (B600 Bq kg1 dry weight) in the sediments immediately under the accident site, but were 10–20 times lower in the remaining deep areas of Bylot Sound. Concentrations of 239,240Pu in edible biota such as squid, fish, and shrimp were one to two orders of magnitude less than those in the sediments. Seawater concentrations in the Bylot Sound were in the range 5–10 mBq 239,240Pu m3. Rocky Flats Nuclear Weapons Plant
Two major fires have occurred at the Rocky Flats Nuclear Weapons Plant, which is situated approximately
25 km from Denver, Colorado. In the first in 1957 spontaneous ignition of 15–20 kg plutonium caused contamination in the plant area. In the second fire in 1969 several kg of plutonium metal combusted spontaneously causing a smoke plume that spread to surrounding areas; releasing B130 GBq, much of it spreading outside the site boundaries. Soil densities of up to 50–70 Bq Pu m2 were found at or beyond the plant perimeter. The Mayak Production Association
Since 1948 this complex, situated in the southern Urals near the town of Kyshtym, Russia and 150 km from Chelyabinsk, has operated seven nuclear reactors and two reprocessing plants and has discharged B100 PBq of fission products, including at least 40 TBq of plutonium, into the Techa River. These discharges, plus the explosion of a large chemical tank in 1957, caused widespread contamination both of the local environment and of some thousands of people. Tomsk, Russian Federation
A further release of some 300 kg of plutonium as a result of the explosion of a tank containing kerosene and tributylphosphate occurred at Tomsk in Siberia in 1993, causing widespread contamination over an area of 120 km2. The Semipalatinsk Nuclear Testing Site
This site, situated in NE Kazakhstan was involved with 86 atmospheric, 30 surface, and 346 underground nuclear tests between 1949 and 1989. Core samples 23 cm in depth indicated depositions of 330 kBq m2 near the hypocenter of the first nuclear test and 1–4 kBq m2 at 5–15 km from ground zero. Measurements in October 2005 within the inhabited village of Dolon, 80 km northeast of the boundary of the test area, showed deposition densities ranging from 0.076 to 40.9 kBq m2 with an average of 6 kBq m2.
Movement of Plutonium from Surface and Sediment Deposits Chemically, plutonium in the fallout from weapons testing was almost all in the form of oxides formed at high temperatures and in the form of small particles. The largely insoluble, plutonium particles deposited on soil surfaces appear to be migrating slowly to depths of up to approximately 40 cm; similar migration is also found in marine and freshwater sediments. Plutonium may be incorporated into plants by direct foliar deposition from the air, either as material carried down in rainfall, or as fine soil particles resuspended by wind and rain with subsequent deposition on the plant. Foliar absorption of the deposited plutonium or uptake from the soil through
Plutonium: Environmental Pollution and Health Effects
the roots may occur; however, in general these processes play minor roles and the major contamination of grassland and leafy food crops comes from foliar deposition of resuspended material. Radionuclide uptake by plants, or other biota, is often expressed as a concentration ratio (CR), defined as the radioactivity per kg dry weight of plant or other material expressed as a fraction of the radioactivity per kg dry weight of soil, per liter of water. Values of CR have been obtained mainly by greenhouse or field studies with quite highly contaminated soils, for example, in the vicinity of reprocessing or other nuclear plants; similarly CR for aquatic species have been obtained from studies in rivers or oceans receiving plutonium discharges from such installations. Direct measurement of CR by studies with biota grown on soils, or in waters, contaminated only by fallout plutonium are often impracticable because the concentrations are near to or below the limits of detection of the analytical method. The data suggest that for natural vegetation, including pastures and leafy vegetables, the CR may range from B0.02 to 0.6, and for cereals, fruits, and root vegetables from 0.0001 to 0.3. For animal products, CRs are much smaller ranging from B2 108 to 1 107 for the transfer from soil, via feed, to eggs, beef, lamb, and lamb or beef liver. Plutonium deposited in the oceans, rivers, and lakes can be taken up by plankton and shellfish and fish that may form part of the human food chain. Table 5 shows the concentrations of 238Pu and 239,240Pu measured in fish muscle collected from the Baltic Sea, which is contaminated by both fallout and Chernobyl-derived plutonium plus a small input from Sellafield discharges. The table also shows the concentrations found in winkles and mussels collected off the coast of Cumbria, UK near the Sellafield reprocessing plant. Table 5 shows that, although concentrations in the commonly eaten fish from the Baltic Sea are o1 mBq kg1, those in the shellfish from the much more highly contaminated waters off Sellafield are three orders of magnitude greater.
Table 5 Concentrations of 238Pu, edible parts of fish and shellfish Species
Location
239,240
Pu observed in the
Concentration (mBq kg1) 238
239,240
0.036
0.13
0.13 0.09 0.027 7000– 27 000 7000– 13 000
0.24 0.29 0.16 31 000– 113 000 31 000– 46 000
Pu
Flounder (muscle) Herring (muscle) Cod (muscle) Sprat (muscle) Winkles Mussels
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Human Exposure to Environmental Plutonium Plutonium can enter the human body by inhalation of contaminated air or by ingestion of contaminated foods or drinking water. The fractional absorption of plutonium from the human gastrointestinal tract is very low, (B1–10) 104 of the ingested activity. The relative intakes by inhalation and ingestion by residents of Finland during the period of high fallout, from 1954 to 1978, are illustrated in Figure 3; in this figure, the intake by ingestion is shown as both the total estimated intake into the alimentary tract and the amounts entering the bloodstream assuming a fractional absorption of 5 104. This figure indicates that inhalation represented the major route of intake with the amounts of 239,240Pu inhaled by the southern Finns and Lapps being broadly similar. Since the air concentrations in Finland were comparable with those recorded for other places in the Northern Hemisphere, this inhalation intake may be regarded as reasonably typical for this hemisphere during this period. In contrast, the amounts ingested by the Lapps were 10–15 times greater than those of the southern Finns; this is due to the very high proportion of reindeer liver and meat in the Lapp’s diet. Reindeer feed on lichens that take up much higher amounts of 239,240Pu than other types of pasture; reindeer liver that constitutes B70% of the Lapps diet, contained up to 400 mBq 239,240 Pu kg1 with much lower concentrations in the meat B5 mBq 239,240Pu kg1. After 1973, the annual ingestion by both groups remained essentially constant. Of the inhaled plutonium, depending on the chemical form of the inhaled material, some will be relatively rapidly cleared from the respiratory tract and swallowed, some will penetrate deep into the lung from where some may be absorbed into the blood, and another fraction may migrate into the alveolar macrophages where it will remain for long periods. The plutonium that is absorbed into the blood, either from the alimentary tract or from the lungs, will deposit mainly in the liver and bone, where it is retained for long periods. The organ distribution of fallout plutonium in the human body can be seen in Figure 4, which shows the median 239,240Pu content of the liver, bone, lungs þ tracheobronchial lymph nodes (TBLN), and the estimated total body content of adult persons who died between 1970 and 1982 in several countries; all of whom had lived throughout the period of maximum fallout activity between 1963 and 1973. The data in Figure 4 suggest that the highest values, B150 mBq, were seen in persons who died in the United States or Japan during the period 1970–75; by the early 1980s, the values appear to have decreased to approximately 50–120 mBq. Calculations suggest that persons born in 1970, or later, will have much smaller body contents of fallout 239,240Pu, o3 mBq; however, such levels
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Plutonium: Environmental Pollution and Health Effects
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Figure 3 Estimated annual intake of 239,240Pu by Lapps and residents of Southern Finland during the period 1955–78. The intake by ingestion is shown as total ingestion into the alimentary tract, and as the amount absorbed into the blood stream assuming a fractional absorption of 0.0005. Data recalculated from that of Mussalo-Rauhamaa H (1981) Accumulation of plutonium from fallout in southern Finns and Lapps. Report Series Radiochemistry 4, University of Helsinki. Total body/organ content (mBq) 0
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Lung+TBLN Liver
Germany, Munich, 1980−81
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Figure 4 The comparative body contents of 239,240Pu in the bones, liver, lungs þ tracheobronchial lymph nodes, other tissues, and total body content of persons who died in various parts of the world between 1970 and 1984. The total height of each column represents the total body content of the individuals in that group.
Plutonium: Environmental Pollution and Health Effects
are difficult to confirm by measurements of autopsy samples, even with the most sensitive methods of analysis that have a detection limit of B0.5 mBq per sample. For radiological protection purposes, the International Commission on Radiological Protection (ICRP) assumes that of the plutonium that enters the blood, 30% will be deposited in the liver and be retained with a half-time of 20 years; a further 50% will deposit in bone and be retained with a half-time of 50 years; the remaining 20% is deposited in the other tissues or excreted. Analysis of the data shown in Figure 4 indicates that the observed median liver and skeleton concentrations account for 37% and 53%, respectively, of the estimated total body content. Individual values ranged from 15% to 66% for liver and 26% to 75% for the skeleton. The data for the years 1970 and 1977 for six states in the United States indicate that the median total body content was decreasing over this time with a biological half-time of B6 years, suggesting that the retention in the body may be less prolonged than that proposed by ICRP. The information on the levels of environmental 238Pu in the human body is sparse, as the concentrations in tissues other than bone are often below the limits of detection of the best available analytical methods. Assuming that the 238Pu content of the skeleton is 60% of the total body content, the measurements on a few persons who died in Colorado or Washington, DC during the period 1977–79, suggest a total body content of B18 mBq, or about one-fifth of that of 239,240Pu. The data for the few residents of west Cumbria, near the Sellafield facility, suggest body contents of approximately 50% higher than those found in the other parts of the United Kingdom. For some people in this area, their plutonium intake is increased by the consumption of locally harvested shellfish (winkle and mussels) and this increases the annual radiation dose they receive from all other environmental sources, B2.6 mSv, by B20 mSv. In some areas, the Chernobyl accident led to further intake of plutonium; for example, estimates for the Bialystok region of Poland suggest that the 239,240Pu body content may have increased by B6 mBq, an increase of approximately 8% over that expected from weapons fallout alone. Studies of persons dying after living for B25 years at up to 8 km from the Mayak complex suggest plutonium body burdens of B3–6 Bq, more than an order of magnitude greater than that expected from fallout plutonium alone.
Potential Health Effects of Environmental Plutonium The high specific activities of 238Pu and 239Pu, 634 kBq mg1 (1.5 pg Bq1) and 2.3 kBq mg1 (434 pg Bq1), respectively, mean that radiotoxic effects will predominate
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over any chemical toxicity. There is, fortunately, little direct information on the radiotoxicity of 238,239Pu in humans and most of the available information comes from studies of exposed workers, who were often also exposed to g rays or other forms of radiation. Studies of the radiotoxicity of 239Pu in experimental animals have demonstrated that inhalation of large activities of either 238Pu or 239Pu can cause acute effects such as radiation pneumonitis, pulmonary fibrosis, bone changes (osteodystrophy), and blood and liver abnormalities. In addition, at lower activities tumors of bone, lung, and liver may arise after latent periods of a few to more than 10 years. There are some differences in the effects of inhaled 238PuO2 and 239PuO2, which result from differences in their biokinetics and radiation dose patterns, which make 238Pu somewhat more mobile than 239Pu. Inhaled plutonium may remain in the lungs or migrate to the bones, liver, or other body organs. Following ingestion of plutonium o0.1% will be absorbed into the bloodstream from where it will be deposited predominantly in the liver and skeleton. Plutonium deposited in liver and bone appears to remain in the body for many years; the fallout data discussed earlier suggest that between 1970 and 1980, the total body content of 239,240 Pu decreased with a half-time of B6 or more years; however, studies in experimental animals intravenously injected with 239Pu suggest biological half-times of up to 40 or more years. The radiotoxicity studies in animals have generally been conducted with activities that were much higher than those encountered by workers, and orders of magnitude greater than those accumulated by members of the general public from the inhalation or ingestion of environmental plutonium. Epidemiological studies, involving 18 833 persons (14 075 males and 4758 females) who worked at the Mayak Production Association from 1948 to 1972 and who were followed up to December 2000, found that 121 cases of pulmonary fibrosis (pneumosclerosis) (65 males and 56 females) had arisen in persons exposed to an average lung dose from plutonium of 4.070.5. Gy plus 0.9370.14 Gy of external g radiation. In addition, 592 lung cancer deaths (532 males and 60 females) were recorded in this period; the data suggesting that a statistically significant, dose-dependent increase in lung cancer mortality was seen with committed effective doses to the respiratory tract Z6.2 Sv. Compared with global environmental levels, these workers inhaled very large amounts of plutonium. The ongoing studies of the Mayak populations appear to provide powerful evidence that plutonium was the most likely cause of some other types of cancer. Long-term medical follow-up of 26 Manhattan project workers with residual body contents of 52–3180 Bq
Plutonium: Environmental Pollution and Health Effects
(median 500 Bq) 239Pu dating from 1944 to 1945 showed some evidence for a preferential reduction in suppressor T-lymphocytes, indicating some potential effects on the immune system; however, the frequency of these aberrations could not be correlated with their plutonium body contents. By the end of 1994, 7 of these 26 workers had died, compared with an expected 13 deaths based on the mortality rates for white males in the general US population. Of the seven deaths, one was accidental, two due to cardiovascular disease, and one due to pneumonia; the remaining three were due to prostate, lung, and bone cancers in subjects with 239Pu body contents of 740, 3080, and 580 Bq, respectively. Among the 19 workers still alive at the end of 1990, three, aged 75–81 years, had been diagnosed with prostate cancer. Based on the age-adjusted incidence rates for prostate cancer in the US white males, the standardized incidence ratio (SIR) for the four cases in this group is 1.8 (95% confidence limits (CL) 0.5–4.6), because the wide 95% CL includes an SIR, the incidence of prostate cancer cannot be regarded as significantly different from that which would have been expected in a nonexposed group of this small size. A total of three lung cancers were found in these 26 workers over the 50 year observation period, the age-adjusted SIR is 1.8 (95% CL 0.4–5.2), which again suggests that the incidence of lung cancer was not significantly increased. The occurrence of the single case of osteosarcoma of the sacrum in the Los Alamos worker group is noteworthy since the animal studies have clearly demonstrated the induction of bone cancers by 239Pu. The presence of this tumor in this small study group is statistically significant when compared with the mortality rates for white US males, or with a group of 876 unexposed Los Alamos workers. However, when this case was included in a larger study involving 3775 plutonium-monitored males who worked at Los Alamos from 1943 to 1977, of whom 303 were exposed with estimated body contents Z74 Bq 239 Pu, it was found that the incidence rate ratios were not significantly different from 1 for bone or any other form of cancer. No bone cancers have been reported among the 5143 plutonium-exposed Rocky Flats workers studied. Neither the epidemiological studies of the Los Alamos or the Rocky Flats workers nor the animal studies identify any minimum levels of plutonium in the human body, or in air, food, or water, which would likely lead to harmful effects. However, for radiological protection purposes, the ICRP recommends adoption of the socalled linear-no-threshold model for the induction of cancers by radiation; this conservative hypothesis assumes that any amount of absorbed radiation, no matter how small, may cause some damage. However, at present there is no good evidence to confirm that this hypothesis holds for the very low radiation doses, generally o10 mSv, likely to be received by workers in
well-regulated workplaces, or by the general public from plutonium released into the environment. Any consideration of the potential health effects of environmental plutonium must also take into account the amounts of the natural a-particle emitting radionuclides that are also inescapably present in the human body, especially those that deposit preferentially in bone (e.g., 238U and 228,230,232Th). Figure 5 compares the total body, liver, and lung contents of 238þ239þ240Pu with those for 234þ235þ238U, and 228þ230þ232Th in the US residents of Colorado who died during 1977–79. Calculation of the total radiation doses delivered by the isotopes deposited in bone, the major tissue of radiological concern, yields dose rates of B2 mSv a1 for the uranium isotopes and B16 mSv a1 for the thorium isotopes and their radioactive daughter products, but only B0.3 mSv a1 for 238þ239þ240Pu. These are very small radiation doses. Assuming the ICRP risk factor for an irradiation-induced cancer of 0.01 Sv1, and an exposure to 10 mSv from plutonium might cause 1 in 10 million chance of inducing a bone tumor: this is about 100 000-fold smaller than the risk of developing a spontaneous (natural) bone tumor. Such a low risk could not be detected by any currently available method and would be considered by most people to be negligible. Thus, it appears very unlikely that the levels of 238Pu and 239,240 Pu currently present in the environment will pose any significant threat to human health. A potential cause for concern is the B1200 tonnes of, now largely unwanted, plutonium that has arisen from the decommissioning of nuclear weapons and from nuclear power production. If even a few kilograms of this plutonium were to fall into the hands of terrorists and be released as a fine aerosol into a crowded building or stadium, this could lead to hundreds, even thousands,
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The comparative body contents of 228þ230þ232Th, U, and 238þ239þ240Pu in the bodies of persons who died in Colorado during the period 1977–79.
Figure 5
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Plutonium: Environmental Pollution and Health Effects
of persons inhaling sufficient activity to cause serious harm within either a relatively short or a very long period. However, assuming that this largely unwanted plutonium can be securely stored, or burnt up in nuclear power reactors (a process that should not increase environmental exposure), and that there is no future nuclear arms race with atmospheric or near surface weapons testing, plutonium in the global environment should pose no future hazard to members of the public. See also: Clinical Consequences of Radiation Exposure, Ionizing Radiation Exposure: Psychological and Mental Health Aspects, Risk to Populations Exposed from Atmospheric Testing and Those Residing Near Nuclear Facilities.
Further Reading Choppin GR, Liljenzin LO, and Rydberg J (1995) Radiochemistry and Nuclear Chemistry. Oxford: Butterworth-Heinemann. Harley JH (1980) Plutonium in the environment: A review. Journal of Radiation Research (Japan) 21: 83--104. International Commission on Radiological Protection (ICRP) (1986) The metabolism of plutonium and related elements. ICRP Publication 48. Annals of the ICRP 16(2/3).
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International Commission on Radiological Protection (ICRP) (2008) Recommendations of the ICRP. ICRP Publication 103. Annals of the ICRP 37(2–4). Kudo A (ed.) (2001) Plutonium in the Environment. Edited Proceedings of the Second Invited International Symposium. Radioactivity in the Environment Series, Volume 1. Elsevier: Amsterdam. Mussalo-Rauhamaa H. (1981) Accumulation of plutonium from fallout in southern Finns and Lapps. Report Series in Radiochemistry 4. University of Helsinki National Council on Radiation Protection and Measurement (NCRP) (2001) Scientific Basis for evaluating the risks to populations from space applications of plutonium. NCRP Report No. 131. Bethesda MD: NCRP. Taylor DM (1995) Environmental plutonium in humans. Applied Radiation and Isotopes 46: 1245--1252. Taylor DM (2002) Radionuclides in the environment. In: Sarkar B (ed.) Heavy Metals in the Environment, pp. 95--120. New York: Marcel Decker. Taylor DM and Taylor SK (1997) Environmental uranium and human health. Reviews of Environmental Health 12: 147--157. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (1993) Sources and effects of ionizing radiation. UNSCEAR 1993 Report to the General Assembly, with Annexes. New York: United Nations. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (2000) Sources and effects of ionizing radiation. UNSCEAR 2000 Report to the General Assembly, with Annexes. Annex J. Exposures and effects of the Chernobyl accident. New York: United Nations.